Entomologists perform role as matchmakers for cerambycid beetles

Aug 16, 2008

Scientists have discovered cheap, generic blends of love potions to attract several species of pest cerambycid beetles.

During a three-year project, University of California Riverside Entomologist Jocelyn Millar and University of Illinois Entomologist Larry Hanks tripled the number of known pheromones that can be used to attract species of pest cerambycids.

Pheromones are chemicals that insects emit to attract mates, and they can be used in traps to more efficiently find and control beetles, especially when populations are at low densities or difficult to survey.

This project was funded by the University of California Exotic/Invasive Pests and Diseases Research Program.

Cerambycid, or longhorned beetles, deposit eggs in protected places on bark. The larvae feed on the inner bark, and then bore into the sapwood or heartwood. Wood-boring beetles in the Cerambycidae family include many species that attack and kill fruit trees, ornamental trees and shrubs, timber, and wood in buildings.

The beetles can also transmit nematodes, fungi, and other pathogens that can kill the host trees. Probably the most well-known and dreaded disease is the pine wilt disease that is caused by the pinewood nematode Bursaphelenchus xylophilu which is vectored by pinesawyer beetles.

This nematode has devastated pine forests in Japan and China, and it is in most U.S. states, see http://nematode.unl.edu/bxyloph.htm[1]. Cerambycids are also likely to transmit pitch canker and other fungal diseases through contamination of feeding and oviposition wounds with fungal spores.

The tunnels made by cerambycid larvae in host trees are roughly circular in cross section, and can be more than 1 inch wide. Some species bore in the sapwood and heartwood, whereas others feed in the cambium layers, effectively destroying the vascular tissues of the tree, and killing branches or the whole tree.

Millar and Hanks have successfully identified pheromone blends for more than 30 species, including several invasive pests. They also have shown that adult beetles of another 10 species apparently do not use pheromones, but rather are attracted by volatile chemicals released by the host trees.

“Little was known about the chemical ecology of cerambycid beetles or their use of attractant pheromones before this project,” Millar said. “The pheromones of only a few species had been identified.”

“Our longer-term goals are to gain a better understanding of which subfamilies, tribes, and genera are likely to use pheromones, and within those groups, to determine the types of chemicals that are used as pheromones,” Millar said. “This will allow us to predict whether new invaders are likely to use pheromones that we can exploit, and if so, what those pheromones are likely to be.”

During the second year of the project, the research group identified two diagnostic characteristics, one behavioral and one morphological, that will allow researchers to immediately assess whether a species is likely to have a male-produced attractant pheromone. The study also found the first examples of powerful female-produced pheromones in the Cerambycidae family.

Millar said, “These morphological features and specific behaviors are reliably associated with pheromone use by cerambycid beetles.

“So, from simply observing the behavior of a new invasive cerambycid species, regulatory personnel can assess whether it uses attractant pheromones that can be identified and exploited for its detection and management.”

The study also showed that many cerambycid species produce large amounts of pheromone (hundreds of micrograms over a few hours).

“This is critically important for lure design, because lures must release 5 to 25 milligrams of pheromone per day to be effective. This is in marked contrast to pheromone lures for other insect species, where release rates are typically a few micrograms per day.

“We are working to develop lures for field use that are capable of these high release rates for extended periods (weeks).”

The UC Exotic/Invasive Pests and Diseases Research Program targets research on exotic pests and diseases in California. The program aims not only to improve our knowledge and management of pests that are already here, but also to reduce the potential impact of those pests and diseases that pose a threat to the state.

The research program is a collaboration between the UC Statewide Integrated Pest Management Program and the UC Riverside Center for Invasive Species Research. The U.S. Department of Agriculture, Cooperative State Research Education and Extension Service funds the program.